1. Field of the Invention
The present invention relates to an air-fuel ratio sensor which measures the air-fuel ratio of the fuel mixture in internal combustion engines from exhaust gas and more specifically to an air-fuel ratio sensor for detecting the air-fuel ratio of the fuel mixture in internal combustion engines from exhaust gas comprising an oxygen ion conductive solid electrolyte, a diffusion resistor, a heater and an electrode. The air-fuel ratio sensor in the present invention can prevent variations in the sensor output with the passage of time due to clogging of the diffusion resistor.
2. Description of the Prior Art
The conventional air-fuel ratio sensor, for example as disclosed in the Japanese Patent Application Laid-Open No. 57050/1983, has its sensor output characteristic corrected according to the detected value when the atmospheric air is measured. However, the above-mentioned conventional air-fuel ratio sensor shows no positive means to prevent the sensor output variations that may occur with the elapse of time.
The above mentioned conventional air-fuel ratio sensor does not propose a means to remove contaminate particles such as carbon, sulfer, dust etc., adhering, to the diffusion resistors, but only considers a means for correcting the sensor output of the air-fuel ratio sensor. So, the conventional air-fuel ratio sensor has a problem in keeping the precision of the air-fuel ratio over a long period of time.
With the conventional system, it is in practice difficult to make sensor output corrections with good accuracy because the sensor output characteristic for the air-fuel ratio is not linear.